Network Working Group X. Li
Internet-Draft C. Bao
Intended status: Experimental CERNET Center/Tsinghua
Expires: April 15, 2013 University
W. Dec
O. Troan
Cisco Systems
S. Matsushima
SoftBank Telecom
T. Murakami
IP Infusion
October 12, 2012
Mapping of Address and Port using Translation (MAP-T)draft-ietf-softwire-map-t-00
Abstract
This document specifies the "Mapping of Address and Port" double
stateless translation based solution (MAP-T) for providing shared or
uniquely addressed IPv4 host connectivity to and across an IPv6
domain,
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 15, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Internet-Draft MAP-T October 20121. Introduction
Experiences from initial IPv6 deployments indicate that transitioning
a network providers' domain fully to IPv6 requires not only the
continued support of legacy IPv4 users connected to the boundary of
that domain, allowing IPv4 address sharing, but also the need for
carrying out IPv6-only operational practices in that domain [, also
for traffic from IPv4 users. The use of an double NAT64 translation
based solutions is an optimal way to address these requirements,
particularly in combination with stateless translation techniques
that seek to minimize challenges outlined in
[I-D.ietf-softwire-stateless-4v6-motivation].
The Mapping of Address and Port - Translation (MAP-T) solution
defined in this document is such a solution, that builds on existing
stateless NAT64 techniques specified in [RFC6145], along with a
stateless algorithmic address & port mapping scheme to allow the
sharing of IPv4 addresses across an IPv6 network. The MAP-T solution
is closely related to MAP-E [I-D.ietf-softwire-map], with both
utilizing the same algorithmic method, but differing in their choice
of translation [RFC6145] and encapsulation [RFC2473]based IPv6
transports.
A companion draft defines the DHCPv6 options for provisioning of MAP
[I-D.mdt-softwire-map-dhcp-option], applicable to both MAP-T and
MAP-E.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Terminology
MAP domain: One or more MAP CEs and BRs connected to the
same IPv6 network. A service provider may
deploy a single MAP domain, or may utilize
multiple MAP domains.
MAP Rule: A set of parameters describing the mapping
between an IPv4 prefix, IPv4 address or
shared IPv4 address and an IPv6 prefix or
address. Each MAP domain uses a different
mapping rule set.
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MAP node: A device that implements MAP.
MAP Border Relay (BR): A MAP enabled router managed by the service
provider at the edge of a MAP domain. A
Border Relay router has at least an IPv6-
enabled interface and an IPv4 interface
connected to the native IPv4 network. A MAP
BR may also be referred to simply as a "BR"
within the context of MAP.
MAP Customer Edge (CE): A device functioning as a Customer Edge
router in a MAP deployment. A typical MAP CE
adopting MAP rules will serve a residential
site with one WAN side interface, and one or
more LAN side interfaces. A MAP CE may also
be referred to simply as a "CE" within the
context of MAP.
Port-set: Each node has a separate part of the
transport layer port space; denoted as a
port-set.
Port-set ID (PSID): Algorithmically identifies a set of ports
exclusively assigned to the CE.
Shared IPv4 address: An IPv4 address that is shared among multiple
CEs. Only ports that belong to the assigned
port-set can be used for communication. Also
known as a Port-Restricted IPv4 address.
End-user IPv6 prefix: The IPv6 prefix assigned to an End-user CE by
other means than MAP itself. E.g.
Provisioned using DHCPv6 PD [RFC3633] or
configured manually. It is unique for each
CE.
MAP IPv6 address: The IPv6 address used to reach the MAP
function of a CE from other CEs and from BRs.
Rule IPv6 prefix: An IPv6 prefix assigned by a Service Provider
for a mapping rule.
Rule IPv4 prefix: An IPv4 prefix assigned by a Service Provider
for a mapping rule.
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The MAP-T BR is responsible for connecting external IPv4 networks to
all devices in one or more MAP-T domains, using stateless NAT64 as
extended by the MAP-T rules in this document.
Besides the CE and BR, the MAP-T domain can contain any regular IPv6-
only hosts/servers that have an IPv4 mapped IPv6 address (IPv4-
translatable address per [RFC6052]) using a prefix assigned to the
MAP-T domain. Communication with such devices is naturally possible
in the MAP-T architecture from inside or outside the MAP-T domain
including from any IPv4-only hosts. In this mode, any IPv6-only
servers SHOULD have both A and AAAA DNS server records. DNS64
[RFC6147] becomes required only when IPv6 servers in the MAP-T domain
are expected themselves to initiate communication to internal/
external IPv4-only entities.
Functionally the MAP-T CE and BR use existing standard functional
building blocks, or extensions to these as follows:
o A standard NAPT [RFC2663] function on a MAP CE is extended with
support for restricting the allowable TCP/UDP ports for a given
IPv4 address. The enforcement of NAPT function, as well as the
port restriction is conditional upon the MAP CE's configuration as
applied by the network operator.
o A standard stateless NAT64 function [RFC6145]is extended for
translating IPv4 traffic to IPv6, based on a lookup of source/
destination IPv4 address + TCP/UDP port or ICMP id information
that is then mapped to the source/destination IPv6 address. This
algorithmic mapping is specified in section 5.
Section 6 describes how these functional blocks are combined with the
Mapping Rules of Section 4 to enable IPv4-IPv6 communication between
the CE and BR and IPv6-only servers in the domain.
5. Mapping Rules
A MAP node is provisioned with one or more mapping rules.
Mapping rules are used differently depending on their function.
Every MAP node must be provisioned with a Basic mapping rule. This
is used by the node to configure its IPv4 address, IPv4 prefix or
shared IPv4 address. This same basic rule can also be used for
forwarding, where an IPv4 destination address and optionally a
destination port is mapped into an IPv6 address or prefix.
Additional mapping rules are specified to allow for e.g. Multiple
different IPv4 subnets to exist within the domain and optimize
forwarding between them.
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Traffic outside of the domain (i.e. When the destination IPv4
address does not match (using longest matching prefix) any Rule IPv4
prefix in the Rules database) will be forward using the Default
mapping rule. The Default mapping rule maps outside destinations to
the BR's IPv6 address or prefix.
In summary, there are three types of mapping rules:
1. Basic Mapping Rule (BMR) - used for configuring the CE's IPv4
address and/or port set assignment as well as deriving the MAP
IPv6 address that the CE is to use. There can only be one Basic
Mapping Rule per End-user IPv6 prefix. The BMR is composed of
the following parameters:
* Rule IPv6 prefix (including prefix length)
* Rule IPv4 prefix (including prefix length)
* Rule EA-bits length (in bits)
* Rule Port Parameters (optional)
2. Forwarding Mapping Rule - used for forwarding in the MAP domain.
The Basic Mapping Rule is also a Forwarding Mapping Rule. Each
Forwarding Mapping Rule will result in an entry in the MRT for
the Rule IPv4 prefix + any port range. The FMR consists of the
following parameters:
* Rule IPv6 prefix (including prefix length)
* Rule IPv4 prefix (including prefix length)
* Rule EA-bits length (in bits)
* Rule Port Parameters (optional)
3. Default Mapping Rule - used for destinations outside the MAP
domain. An IPv4 0.0.0.0/0 entry is installed in the MRT for this
rule.
* IPv6 prefix of the BR
* Rule BR IPv4 address (Optional - can be used for testing a
BR's reachability)
A MAP node finds its Basic Mapping Rule by doing a longest match
between the End-user IPv6 prefix and the Rule IPv6 prefix in the
Mapping Rule database. The rule is then used for IPv4 prefix,
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address or shared address assignment.
A MAP IPv6 address is formed from the BMR Rule IPv6 prefix. This
address MUST be recognized by the MAP node, typically a CE, and used
to terminate all MAP traffic received by the node.
Port-aware IPv4 entries in the MRT are installed for all the
Forwarding Mapping Rules and an IPv4 default route for the Default
Mapping Rule.
In hub and spoke mode, all traffic MUST be forwarded using the
Default Mapping Rule.
5.1. Basic mapping rule (BMR)
The BMR is used in combination with the CE's IPv6 prefix to derive
the MAP IPv4 address, port-set and also the MAP IPv6 address. The
structure of a MAP CE's IPv6 address is shown below, along with the
Interface-identifer that is defined in Section 5.4.
| p bits | | q bits |
+----------+ +------------+
|IPv4 sufx| |Port-Set ID |
+----------+ +------------+
\ / ____/ ________/
\ : __/ _____/
\ : / /
| n bits | o bits | s bits | 128-n-o-s bits |
+--------------------+-----------+---------+------------+----------+
| Rule IPv6 prefix | EA bits |subnet ID| interface ID |
+--------------------+-----------+---------+-----------------------+
|<--- End-user IPv6 prefix --->|
Figure 2: IPv6 address format
The Rule IPv6 prefix is the part of the End-user IPv6 prefix (i.e.
the regular IPv6 prefix or address that is assigned to any IPv6
device) that is common among all CEs within the MAP domain. The
Embedded Address bits (EA bits) are the unique per end user within
that Rule IPv6 prefix (some readers may want to think of these as
"MAP customer identifier" bits for a given MAP domain covered by the
Rule IPv6 prefix). When present, the EA bits encode the CE specific
full or part of an IPv4 prefix or address, and in the shared IPv4
address case contain a Port-Set Identifier (PSID) that ultimately
determines the allowed port-range for the CE. An EA-bit length of 0
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IPv4 prefix:
| r bits | p bits |
+-------------+---------------------+
| Rule IPv4 | IPv4 Address suffix |
+-------------+---------------------+
| < 32 bits |
Figure 5: IPv4 prefix
The length of r MAY be zero, in which case the complete IPv4 address
or prefix is encoded in the EA bits. If only a part of the IPv4
address/prefix is encoded in the EA bits, the Rule IPv4 prefix is
provisioned to the CE by other means (e.g. a DHCPv6 option). To
create a complete IPv4 address (or prefix), the IPv4 address suffix
(p) from the EA bits, are concatenated with the Rule IPv4 prefix (r
bits).
The offset of the EA bits field in the IPv6 address is equal to the
BMR Rule IPv6 prefix length. The length of the EA bits field (o) is
given by the BMR Rule EA-bits length. The sum of the Rule IPv6
Prefix length and the Rule EA-bits length MUST be less or equal than
the End-user IPv6 prefix length.
If o + r < 32 (length of the IPv4 address in bits), then an IPv4
prefix is assigned.
If o + r is equal to 32, then a full IPv4 address is to be assigned.
The address is created by concatenating the Rule IPv4 prefix and the
EA-bits.
If o + r is > 32, then a shared IPv4 address is to be assigned. The
number of IPv4 address suffix bits (p) in the EA bits is given by 32
- r bits. The PSID bits are used to create a port-set. The length
of the PSID bit field within EA bits is: o - p.
The length of r MAY be 32, with no part of the IPv4 address embedded
in the EA bits. This results in a mapping with no dependence between
the IPv4 address and the IPv6 address. In addition the length of o
MAY be zero (no EA bits embedded in the End-User IPv6 prefix),
meaning that also the PSID is provisioned using e.g. The DHCP
option.
In the following examples, only the suffix (last 8 bits) of the IPv4
address is embedded in the EA bits (r = 24), while the IPv4 prefix
(first 24 bits) is given in the BMR Rule IPv4 prefix.
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0.0.0.0/0 (Rule IPv4 prefix)}
Example: Default Mapping Rule
The Deafult Rule's IPv6 prefix is combined by a MAP-T CE with the
IPv4 destination addresses, using RFC6052, to form a full IPv6
destination address for any IPv4 destination following the IPv4
default route. Figure 7 below shows such an address format. Note
that the BR prefix-length is variable and can be both shorter or
longer than 64 bits, up to 96 bits. In the respective cases the IPv4
address and the BR prefix are shifted and "bit spread" across the
fixed u-octet boundary as per [RFC6052]. All trailing bits after the
IPv4 address are set to 0x0.
<---------- 64 ------------>< 8 ><----- 32 -----><--- 24 --->
+--------------------------+----+---------------+-----------+
| BR IPv6 prefix | u | IPv4 address | 0 |
+--------------------------+----+---------------+-----------+
Figure 7: IPv6-IPv4 Mapped Address
5.4. MAP IPv6 Interface Identifier
The IPv6 Interface identifier format of a MAP node is based on the
format specified in section 2.2 of [RFC6052], with the added PSID
field if present, as shown in Figure 8.
+--+---+---+---+---+---+---+---+---+
|PL| 8 16 24 32 40 48 56 |
+--+---+---+---+---+---+---+---+---+
|64| u | IPv4 address | PSID | 0 |
+--+---+---+---+---+---+---+---+---+
Figure 8: MAP IPv6 Interface Identifier
The encoding of the full IPv4 address into the interface identifier
into the IPv6 addresses have been shown to be useful for
troubleshooting.
In the case of an IPv4 prefix, the IPv4 address field is right-padded
with zeros up to 32 bits. The PSID field is left-padded to create a
16 bit field. For an IPv4 prefix or a complete IPv4 address, the
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PSID field is zero.
5.5. Port mapping algorithm
The Generalized Modulus Algorithm (GMA) is used in MAP domains whose
rules allow IPv4 address sharing. Each CE in such a domain has an
IPv4 address and a unique Port-Set Identifier (PSID), that is derived
by means of the BMR. For a given IPv4 address, the algorithm allows
each PSID to be processed to reveal a set of unique non-overlapping
ports, or alternatively for any given port to derive the PSID it
corresponds to. Two extreme cases supported by algorithm are: (1)
the port numbers are not contiguous for each PSID, but uniformly
distributed across the port range (0-65535); (2) the port numbers are
contiguous in a single range for each PSID.
For a given sharing ratio (R) and the maximum number of contiguous
ports (M), the GMA algorithm is defined as:
1. The port (P) of a given PSID (K) is composed of:
P = R * M * j + M * K + i
Where:
* PSID: K = 0 to R - 1
* Port range index: j = (4096 / M) / R to ((65536 / M) / R) - 1,
if the port numbers (0 - 4095) are excluded.
* Contiguous Port index: i = 0 to M - 1
2. The PSID (K) of a given port number (P) is determined by:
K = (floor(P/M)) % R
Where:
* % is the modulus operator
* floor(arg) is a function that returns the largest integer not
greater than arg.
5.5.1. Bit Representation of the Algorithm
Given a sharing ratio (R=2^k), the maximum number of contiguous ports
(M=2^m), for any PSID (K) and available ports (P) can be represented
as:
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Example 2: with offset = 0 (a = 0)
5.5.3. GMA Excluded Ports
By default the GMA ensures that a number of "well known" ports are
excluded from use by the algorithm. This number is determined by the
number of offset bits (a), in the figure above. This value can be
optionally provisioned via the "Rule Port Mapping Parameters" in the
Basic Mapping Rule. In the absence of such provisioning, the
defaults are:
o Excluded ports : 0-4095
o Offset bits (a) : 4
For (a) offset bits, the range of excluded ports is 0 to 2 ^ (16-a) -
1.
6. Packet Forwarding
The mapping rules and architectual building blocks are combined at
the CE and BR to enable IPv4-IPv6 communication as follows.
6.1. IPv4 to IPv6 at the CE
A MAP-T CE receiving IPv4 packets SHOULD perform NAT44 function first
and create appropriate NAT44 stateful bindings. The resulting IPv4
packets MUST contain the source IPv4 address and source transport
port number assigned to the CE by means of the MAP Basic Mapping Rule
(BMR).
The IPv4 traffic is subject to a longest IPv4 address + port match
MAP rule selection using the MRT, which then determines the
subsequent NAT64 operation. By default, all traffic is matched to
default mapping rule (DMR), and subject to the stateless NAT64
operation using the DMR parameters for the MAP algorithm and NAT64.
An optional mapping rule, known as a forward mapping rule (FMR), can
be used when forwarding to destinations that correspond to a specific
IPv4+port range in the MAP-T domain i.e. Typically the IPv4 address
and port range of another MAP-T CE, aka mesh-mode. Traffic that is
matched to such a rule is subject to the stateless NAT64 operation
using the FMR parameters for the MAP algorithm and stateless NAT64.
A MAP-T CE MUST support a default mapping rule and SHOULD support one
or more forward mapping rules.
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Internet-Draft MAP-T October 20126.2. IPv6 to IPv4 at the CE
A MAP-T CE receiving an IPv6 packet performs its regular IPv6
operations, whereby only packets that are addressed to the MAP-T BMR
addresses are forwarded to the CE's stateless NAT64 function. All
other IPv6 traffic SHOULD be forwarded as per the CE's IPv6 routing
rules. The CE SHOULD check that MAP-T received packets' transport-
layer destination port number is in the range configured by MAP for
the CE and the CE SHOULD drop any non conforming packet and respond
with an ICMPv6 "Address Unreachable" (Type 1, Code 3).
The CE's stateless NAT64 function MUST derive the IPv4 source and
destination addresses as per Section 5 of this document and MUST
replace the IPv6 header with an IPv4 header in accordance with
[RFC6145]. The resulting IPv4 packet is then forwarded to the CE's
NAPT function, when this is enabled, where the destination IPv4
address and port number MUST be mapped to their original value,
before being forwarded according to the CE's regular IPv4 rules.
When the NAPT function is not enabled, the traffic from the stateless
NAT64 function is directly forwarded according to the CE's IPv4
rules.
6.3. IPv6 to IPv4 at the BR
A MAP-T BR receiving IPv6 packets MUST select a best matching MAP
rule based on a longest address match of the packets' source address
against the BR's configured MAP BMR prefix(es), as well as a match of
the packet destination address against the configured FMR prefix(es).
The selected MAP rule allows the BR to determine the CE's range from
the port-set-id contained in the source IPv6 address. The BR MUST
perform a validation of the consistency of the source against the
allowed values from the identified port-range port. If the packets
source port number is found to be outside the range allowed for this
CE-index and the BMR, the BR MUST drop the packet and respond with an
ICMPv6 "Destination Unreachable, Source address failed ingress/egress
policy" (Type 1, Code 5).
The BR MUST derive the source and destination IPv4 addresses as per
Section 5 of this document and translate the IPv6 to IPv4 headers
following [RFC6145]. The resulting IPv4 packets are then passed to
regular IPv4 forwarding by the BR.
6.4. IPv4 to IPv6 at the BR
A MAP-T BR receiving IPv4 packets uses a longest match IPv4 + port
lookup to select the target MAP-T domain and rule. The BR MUST then
derive the IPv6 source and destination addresses from the IPv4 source
and destination address and port as per Section 5 of this document.
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Following this, the BR MUST translate the IPv4 to IPv6 headers
following [RFC6145]. The resulting IPv6 packets are then passed to
regular IPv6 forwarding.
Note that the operation of a BR when forwarding to MAP-T domains that
do not utilize IPv4 address sharing, is the same as stateless IPv4/
IPv6 translation.
7. ICMP Handling
ICMP messages need to be supported in MAP-T domain and also across
it, taking into consideration also the NAPT component and best
current practice documented in [RFC5508] along with some additional
specific considerations.
MAP-T CEs and BRs MUST follow ICMP/ICMPv6 translation as per
[RFC6145], with the following extension to cover the address sharing/
port-range feature.
Unlike TCP and UDP, which each provide two port fields to represent
both source and destination, the ICMP/ICMPv6 [RFC0792], [RFC4443]
Query message header has only one ID field which needs to be used to
identify a sending IPv4 host.
When receiving IPv4 ICMP messages, the MAP-T CE SHOULD rewrite the ID
field to a port value derived from the Port-set-id. A BR MUST
translate the resulting ICMPv6 packets back to ICMP preserving the ID
field on its way to an IPv4 destination.
In the return path, when MAP-T BR receives an ICMP packet containing
an ID field which is bound for a shared address in the MAP-T domain,
the MAP-T BR SHOULD use the ID value as a substitute for the
destination port in determining the IPv6 destination address. In all
other cases, the MAP-T BR MUST derive the destination IPv6 address by
simply mapping the destination IPv4 address without additional port
info.
If a MAP BR receives an ICMP error message on its IPv4 interface, the
MAP BR should translate the ICMP message to an appropriate ICMPv6
message, as per [RFC6145] and forward it to the intended MAP CE with
the following considerations. If IPv4 address is not shared, the MAP
BR generates a CE IPv6 address from the IPv4 destination address in
the ICMP error message and encapsulates the ICMP message in IPv6. If
the IPv4 address is shared, the MAP BR derives an original IPv4
packet from the ICMP payload and generates a CE IPv6 address from the
source address and the source port in the original IPv4 packet.
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Internet-Draft MAP-T October 20128. Fragmentation and Path MTU Discovery
Due to the different sizes of the IPv4 and IPv6 header, handling the
maximum packet size is relevant for the operation of any system
connecting the two address families. There are three mechanisms to
handle this issue: Path MTU discovery (PMTUD), fragmentation, and
transport-layer negotiation such as the TCP Maximum Segment Size
(MSS) option [RFC0897]. MAP uses all three mechanisms to deal with
different cases.
8.1. Fragmentation in the MAP domain
Translating an IPv4 packet to carry it across the MAP domain will
increase its size by 20 bytes respectively. It is strongly
recommended that the MTU in the MAP domain is well managed and that
the IPv6 MTU on the CE WAN side interface is set so that no
fragmentation occurs within the boundary of the MAP domain.
Fragmentation in MAP-T domain is to be handled as described in
section 4 and 5 of [RFC6145].
8.2. Receiving IPv4 Fragments on the MAP domain borders
Forwarding of an IPv4 packet received from the outside of the MAP
domain requires the IPv4 destination address and the transport
protocol destination port. The transport protocol information is
only available in the first fragment received. As described in
section 5.3.3 of [RFC6346] a MAP node receiving an IPv4 fragmented
packet from outside has to reassemble the packet before sending the
packet onto the MAP link. If the first packet received contains the
transport protocol information, it is possible to optimize this
behavior by using a cache and forwarding the fragments unchanged. A
description of this algorithm is outside the scope of this document.
8.3. Sending IPv4 fragments to the outside
If two IPv4 host behind two different MAP CE's with the same IPv4
address sends fragments to an IPv4 destination host outside the
domain. Those hosts may use the same IPv4 fragmentation identifier,
resulting in incorrect reassembly of the fragments at the destination
host. Given that the IPv4 fragmentation identifier is a 16 bit
field, it could be used similarly to port ranges. A MAP CE SHOULD
rewrite the IPv4 fragmentation identifier to be within its allocated
port set.
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Internet-Draft MAP-T October 20129. Usage Considerations9.1. Hub and spoke with per subscriber rules
Existing IPv4 service can be realized with MAP using a mapping rule
per subscriber. By embedding no part of the IPv4 address in the IPv6
prefix, no dependency between the two address families is created.
This may be useful in cases where the IPv6 address allocation is
sparse, or for other reasons it is difficult to create efficient
mapping rules.
The operator has to the choice of provisioning a full IPv4 address to
the end-user, or a shared IPv4 address by also provisioning the PSID
in the DHCPv6 option. A hybrid of this use case is to provision the
full IPv4 address in the DHCPv6 option, while embedding the PSID in
the IPv6 prefix. That will result in one mapping rule per IPv4
address, e.g. With a sharing ratio of 64, one rule per 64 customers.
9.2. Communication with IPv6 servers in the MAP-T domain
MAP-T allows communication between both IPv4-only and any IPv6
enabled end hosts, with native IPv6-only servers which are using
IPv4-mapped IPv6 address based on DMR in the MAP-T domain. In this
mode, the IPv6-only servers SHOULD have both A and AAAA records in
DNS [RFC6219]. DNS64 [RFC6147] become required only when IPv6
servers in the MAP-T domain are expected themselves to initiate
communication to external IPv4-only hosts.
9.3. Backwards compatibility
A MAP-T CE, in all configuration modes, is by default compatible with
regular [RFC6146] stateful NAT64 devices that are configured to use/
advertise BR prefixes. This allows the use of MAP-T CEs in
environments that require statistical multiplexing of IPv4 addresses
while being able to compromise on the stateful nature. Furthermore,
a MAP-T CE configured to operate without address sharing (no PSID) is
compatible with any stateless NAT64 [RFC6146] devices positioned as
BRs.
10. IANA Considerations
This specification does not require any IANA actions.
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Spoofing attacks: With consistency checks between IPv4 and IPv6
sources that are performed on IPv4/IPv6 packets received by MAP
nodes, MAP does not introduce any new opportunity for spoofing
attacks that would not already exist in IPv6.
Denial-of-service attacks: In MAP domains where IPv4 addresses are
shared, the fact that IPv4 datagram reassembly may be necessary
introduces an opportunity for DOS attacks. This is inherent to
address sharing, and is common with other address sharing
approaches such as DS-Lite and NAT64/DNS64. The best protection
against such attacks is to accelerate IPv6 enablement in both
clients and servers so that, where MAP is supported, it is less
and less used.
Routing-loop attacks: This attack may exist in some automatic
tunneling scenarios are documented in [RFC6324]. They cannot
exist with MAP because each BRs checks that the IPv6 source
address of a received IPv6 packet is a CE address based on
Forwarding Mapping Rule.
Attacks facilitated by restricted port set: From hosts that are not
subject to ingress filtering of [RFC2827], some attacks are
possible by an attacker injecting spoofed packets during ongoing
transport connections ([RFC4953], [RFC5961], [RFC6056]. The
attacks depend on guessing which ports are currently used by
target hosts, and using an unrestricted port set is preferable,
i.e. Using native IPv6 connections that are not subject to MAP
port range restrictions. To minimize this type of attacks when
using a restricted port set, the MAP CE's NAT44 filtering behavior
SHOULD be "Address-Dependent Filtering". Furthermore, the MAP CEs
SHOULD use a DNS transport proxy function to handle DNS traffic,
and source such traffic from IPv6 interfaces not assigned to
MAP-T. Practicalities of these methods are discussed in Section5.9 of [I-D.dec-stateless-4v6].
[RFC6269] outlines general issues with IPv4 address sharing.
12. Contributors
Mohamed Boucadair, Gang Chen, Maoke Chen, Wojciech Dec, Xiaohong
Deng, Jouni Korhonen, Tomasz Mrugalski, Jacni Qin, Chunfa Sun, Qiong
Sun, Leaf Yeh.
The following are the authors who provided a major contribution to
this document:
Li, et al. Expires April 15, 2013 [Page 21]